Mainly that they are old, highly undermaintained and lack features that DB_File and BerkeleyDB ship with.

Another issue is that you might not really use the version you think you use, as many Linux systems ship with compatability libraries nowadays (if available at all). GDBM_File might be what you expect it to be, but likely that the libraries for ndbm are not what you think they are. odbm and sdbm are getting rare.